MC9S12XHZ - GPIO electric schem

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MC9S12XHZ - GPIO electric schem

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sleeperkb
Contributor I
I only beginer. Where i can find electric schem of GPIO (i use MC9S12XHZ). I need to calculate external resistor & capasitor of input.

Alban Edit: FPN in subject

Message Edited by Alban on 2007-03-14 11:31 AM

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sleeperkb
Contributor I
Thanks.
I discussed this with my colleague. I offer clamped diodes on input, when he says that resistror current limiting is enough.
I prefer diodes on input.


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Alban
Senior Contributor II
Hi,
 
Yes, I think it is safer to treat the signal externally and keep the internal clamping diodes for their initial protection purpose.
 
Any other trouble, don't hesitate to ask !
 
Cheers,
Alban.
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sleeperkb
Contributor I
New question similar to the subject. In electrical characteristics maximum input voltage is 6.0 V But i've seen schemes there about 7 volts can be aplied to input pin. Is these schemas is wrong or it is normal practice?
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Alban
Senior Contributor II
Hello,
 
You should not work under "Absolute Maximum Ratings".
The MCU is not made to work in these conditions, just not explode.
 
The MCU is made to work within the operating conditions, which should be 5V +/-10%.
If you go higher on an input, you will inject current, that is bad practise and there is a limit (also in the databook) after which the device will be destroyed also.
 
So, during operating conditions, it's not 6V or 7V, but Supply Voltage +/- 0.5V (a diode threshold voltage).
 
Alban.
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sleeperkb
Contributor I
Sory, but i don't find input resistance in manual. If 5V applied to the pin, what current will flow?
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Steve
NXP Employee
NXP Employee
Since the input is effectively onto the gate of a CMOS transistor almost no current will flow, but your answer is still in the table. It depends on whether you have pull resistors enabled and whether you are accounting for input leakage etc.
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Steve
NXP Employee
NXP Employee
Have a look in the "Electrical Characteristics" section of the Data Book. There you will find the electrical specs of the input and output stages.

Message Edited by Steve on 2007-03-0904:08 PM

Message Edited by Steve on 2007-03-0904:30 PM

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